Lead frame and method of fabricating the same

ABSTRACT

A lead frame is provided, including one or more power terminals and one or more control terminals, wherein at least one of the control terminals is externally terminated with a press-fit contact member, and wherein at least one of the control terminals and at least one power terminals are formed from different materials. With the disclosed lead frame of the invention, lower material cross sections in the power terminals will be provided because of the better electrical conductivity when using pure copper compared to alloys with higher mechanical strengths. Also specific/different plating could be added to the individual needs of the different pin types without using masks in the plating process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits under U.S.C. § 119 toGerman Patent Application No. DE102016112289.0 filed on Jul. 5, 2016,the content of which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

Embodiments of the present invention generally relate to the technicalfield of circuit package; and more particularly, to a lead frame forpackage of electrical power module, and to associated method offabricating the same.

BACKGROUND ART

In the prior art, the use of a lead frame in constructing asemiconductor power module is well known. The external contacts requiredin a finished module are initially stamped from a single sheet of metal.This structure is the lead frame. All the contacts leads are present andconnected together to provide a single structure for convenient handlingand placement. The lead frame is placed on a substrate of a power moduleand connections are in turn made by a semiconductor deviceinterconnection method, such as soldering, sintering, ultrasonicwelding, and so on. Before or after such step the substrate may also bepopulated with electronic components for constituting the power module,such as switching semiconductors (e.g., IGBTs, MOSFETs), passiveelectronic components including resistors, diodes, capacitors orinductors, and interconnections (e.g., as wire-bonds). Then thesubstrate, the electronic components and the lead frames may beencapsulated in an integral circuit package with some of the lead framematerial being removed to leave the leads separated, e.g., by acutting/trimming process.

In a typical current-switching power module, there may be two types ofconnections: i.e., power leads for carrying high currents into and outof the module; and control leads for carrying low-level control signals,for example, to control the functions of input, output and switchover ofthe circuit within the module. An increasingly popular known method ofconnecting the control leads to other circuits within same electronicequipment which comprises the power module, is by the use of press-fitconnectors/terminals. Press-fit terminals are typically shaped at theends of the control leads to form as individual compliant pin sectionswith elasticity which allow for being pushed tightly into and sustaininga permanent contact normal force with corresponding plated through holes(PTH), due to respective deformations of the compliant pin sectionsduring insertion, so as to ensure a reliable electrical and mechanicalconnection over lifetime; however, such press-fit technology is onlysuitable for low-current applications such as passing control signals,rather than for high-current applications e.g., the power connections.In order to maximize the utility of a lead frame in carrying both powersupply current and low-level control signal simultaneously, a pluralityof control leads with elastic/compliant press-fit pins and a pluralityof power leads with high current-carrying capability are combined intoone and the same integral lead frame; and since only one lead frame ofone material is usually used in a molded module, then, such integrallead frame is formed e.g., by using a conductive material havingelasticity. By way of example, a lead frame module including bothpress-fit control leads and non press-fit power leads is shown in in anearlier Korean patent application document KR20110092779.

However, if a single lead frame formed by only one material is to beused, then a compromise has to be reached, leading to power leads thathave a greater than optimum electrical resistance and press-fit leadswhich do not have optimum characteristics, due to different requirementsof the power and control leads. To be specific, it is an advantage ifthe power leads have low electrical resistance and thus a highelectrical conductivity to conduct currents up to several hundred amps;hereby, such power leads are typically made of pure copper. However, incontrast, the control leads with press-fit connectors need to be madefrom a material that has a certain amount of elasticity (high tensilestrength), and pure copper is less suitable than other alloys. Forexample, a typical press-fit type pin needs to be formed by a copperalloy with high mechanical strength and also with a much lowerelectrical conductivity than pure copper. This pin type is usually usedfor auxiliary functions. The lower electrical conductivity of suchsingle elastic material would lead to higher material cross sections forthe power terminals, and in turn a thicker or wider terminal geometries,which needs space in the module and adds part cost accordingly.

In conclusion, on one hand, if a single lead frame is to be formed byone single metallic material, then the requirement for the material isdemanding in both high electrical conductivity and good elasticity.

On the other hand, press fit type pins cannot be provided if highelectrical conductivity is the leading requirement.

In addition, it is sometimes advantageous to plate some contacts in aparticular way. For example, press-fit connectors can be applied with anickel/tin (NiSn) plating, but this is a complex process if a masking isrequired to prevent the plating covering the power connectors.

In order to combine both press-fit pins as control terminals and powerterminals with high current carrying capability into one single moldmodule as an integral lead frame, it is advantageous to use differentmaterials for each pin type. The use of different materials fordifferent pin types helps to tailor the properties like high tensilestrength for the press-fit type and high current carrying capability forthe power terminals. Therefore, it may be advantageous to develop a leadframe with power leads of one highly conductive material and press-fitcontrol leads of another elastic conductive material. In particular,such lead frame may be obtained by combining at least two sub-leadframes of different materials, so that only one assembly lead frame hasto be processed finally the same as previous lead frame in the priorart, while maintaining existing molding, trimming and forming processes.

SUMMARY

The present invention has been made to overcome or alleviate at leastone aspect of the above mentioned disadvantages and/or shortcomingsexisting in the conventional technical solutions.

Accordingly, it is a major object of the exemplary embodiment of thepresent invention to provide a lead frame that leads to lower materialcross sections in the power terminals because of the better electricalconductivity when using pure copper compared to alloys with highermechanical strengths. Also specific/different plating could be added tothe individual needs of the different pin types without using masks inthe plating process.

According to an aspect of the exemplary embodiment of the presentinvention, there is provided a lead frame, comprising one or more powerterminals and one or more control terminals, and at least one of thecontrol terminals is externally terminated with a press-fit contactmember, while at least one of the control terminals and at least onepower terminals are formed from different materials.

According to another exemplary embodiment of the present invention, thelead frame comprises at least one power sub lead frame which is formedby a first material with high current conductivity and at least onecontrol sub lead frame which is formed by a second material withelasticity for making press-fit type terminals thereof, and at least onepower sub lead frame and at least one control sub lead frame arecombined together at a bimetallic interface.

According to another exemplary embodiment of the present invention, thepower sub lead frame and the control sub lead frame which abut eachother are bonded together at the bimetallic interface.

According to another exemplary embodiment of the present invention, thepower sub lead frame and the control sub lead frame are bonded togetherby any one chosen from a group comprising laser welding, ultrasonicwelding, cladding, or use of epoxy resins.

According to another exemplary embodiment of the present invention, oneof the sub lead frames is formed to be provided with a pocket at theends for receiving full profile of corresponding portion of the othersub lead frame.

According to another exemplary embodiment of the present invention, thepower sub lead frame and the control sub lead frame are bonded togetherby any one chosen from a group comprising laser welding, ultrasonicwelding, cladding, or use of epoxy resins.

According to another exemplary embodiment of the present invention,edges of the power sub lead frame and the control sub lead frame at thebimetallic interface are formed to be complementarily profiled along thebimetallic interface, by having respective concave/convex portions whichare complement in shape.

According to another exemplary embodiment of the present invention, thepower sub lead frame and the control sub lead frame are bonded togetherby any one chosen from a group comprising laser welding, ultrasonicwelding, cladding, or use of epoxy resins.

According to another exemplary embodiment of the present invention, oneof the sub lead frames is formed to be provided with a pocket at theends for receiving full profile of corresponding portion of the othersub lead frame, along all of the complementarily profiled edges of thepower sub lead frame and the control sub lead frame.

According to another exemplary embodiment of the present invention, thepower sub lead frame and the control sub lead frame are bonded togetherby any one chosen from a group comprising laser welding, ultrasonicwelding, cladding, or use of epoxy resins.

According to another exemplary embodiment of the present invention, thethickness of the first and second materials is essentially the same.

According to another aspect of the exemplary embodiment of the presentinvention, there is further provided with a method for fabricating alead frame, comprising steps of: manufacturing a control sub lead frameand a power sub lead frame individually and separately; forming one ormore power terminals within the power sub lead frame and one or morecontrol terminals within the control sub lead frame, individually;terminating at least one of the control terminals externally with apress-fit contact member; and abutting, fitting and bonding the two sublead frames together to form a secured bimetallic interface therebetweenso as to form an integral lead frame, and at least one of the controlterminals and at least one power terminals are formed from differentmaterials.

According to an exemplary embodiment of the present invention, the stepof forming terminals further comprises: terminating at least one of thecontrol terminals internally with a control contact member; andterminating at least one of the power terminals internally with a powercontact member.

According to an exemplary embodiment of the present invention, the stepof manufacturing the two sub lead frames comprises providing a pocket atan end thereof along the bimetallic interface for receiving full profileof corresponding portion of the other sub lead frame.

According to an exemplary embodiment of the present invention, the stepof manufacturing the two sub lead frames comprises forming edges of thepower sub lead frame and the control sub lead frame at the bimetallicinterface to be complementarily profiled along the bimetallic interface,by having respective concave/convex portions which are complement inshape.

According to an exemplary embodiment of the present invention, the stepof abutting, fitting and bonding the two sub lead frames togethercomprises bonding by any one chosen from a group comprising laserwelding, ultrasonic welding, cladding, or use of epoxy resins.

According to another exemplary embodiment of the present invention, thelead frame comprises a power sub lead frame which is formed by a firstmaterial with high current conductivity and a control sub lead framewhich is formed by a second material with elasticity for makingpress-fit type terminals thereof, and the power sub lead frame and thecontrol sub lead frame are combined together at a bimetallic interface.

According to another exemplary embodiment of the present invention, thethickness of the first and second materials is essentially the same.

In conclusion, in the solution exemplary embodiments of the presentinvention, a novel and advantageous lead-frame, a package of a powermodule comprising the lead-frame and a method for fabricating the sameare provided by using different materials for each pin type, having someadvantageous technical effects, as below: firstly, the use of differentmaterials for different pin types helps to tailor the properties likehigh tensile strength for the press-fit type signal terminals or controlterminals and high current carrying capability and electricalconductivity property for the power terminals, therefore the lead-framematerial may not necessarily be any one specific alloy material whichhas to make compromise between electrical resistance and mechanicalstrength. Secondly, in the power terminals, low material cross sectionscan be realized because of the better electrical conductivity ascompared with alloys with higher mechanical strengths; meanwhile, aminimized dimensional difference between the power terminals and thecontrol or signal terminals may advantageously balance between the powerterminals and the control or signal terminals the distribution of notonly internal stresses but also any external forces applied thereon,respectively. Thirdly, several different plating processes could also beincorporated during fabrication of a lead-frame as a function of theindividual needs of the different pin types, without the need of masksin the plating process. Finally, since such lead-frame can be achievede.g. by combining at least two or more sub-lead frames to one part sothat only one assembled lead frame has to be processed same as partsmade of prior art, hereby, an advantage of this can be obtained suchthat the molding, trimming, and pin-forming processes still remain thesame as that of the conventional lead-frame processing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a schematic perspective view illustrating a final product ofpower electronic device including a lead frame with power pins andauxiliary pins extending therefrom, in the prior art;

FIG. 2 is a schematic top view of a conventional lead frame in the priorart, before placing onto a substrate of a power electronic device;

FIG. 3 is a schematic top view of an exemplary lead frame with a powersub lead frame and a control sub lead frame which are formed bydifferent metallic materials in an exemplary embodiment of theinvention, before placing onto a substrate of a power electronic device;

FIG. 4(a)-4(g) are schematic top views illustrating the method ofattaching a semiconductor chip onto a substrate while forming individualfinal power terminals and control terminals, by using the exemplary leadframe in FIG. 3;

FIG. 5(a) illustrates a partially enlarged schematic cross-sectionalview of the lead frame as illustrated in FIG. 3, at its bimetallicinterface 106 where the power sub lead frame and the control sub leadframe are bonded directly together, according to an embodiment of thepresent invention;

FIG. 5(b) illustrates a partially enlarged schematic cross-sectionalview of the lead frame as illustrated in FIG. 3, at its bimetallicinterface 106 where the power sub lead frame and the control sub leadframe are bonded together by inserting free end portions of one sub leadframe into the profiles of free end portions of another sub lead frames,according to another embodiment of the present invention;

FIG. 6(a) illustrates a partially enlarged schematic top view of abimetallic interface 106 of lead frame as illustrated in FIG. 3, wherethe power sub lead frame and the control sub lead frame are firstlyfitted with each other positively and then bonded together, according tostill another embodiment of the present invention;

FIG. 6(b) illustrates a partially enlarged schematic top view of abimetallic interface 106 of lead frame as illustrated in FIG. 3, wherethe power sub lead frame and the control sub lead frame are firstlyfitted with and inserted into the profiles of each other, positively,and then bonded together, according to yet another embodiment of thepresent invention;

FIG. 7 illustrates a flow chart of a method for fabricating an exemplarylead frame by two different metallic materials; and

FIG. 8 is a schematic top view of a further exemplary lead frame with apower sub lead frame and a control sub lead frame which are formed bydifferent metallic.

The scope of the present invention will in no way be limited to thesimply schematic views of the drawings, the number of constitutingcomponents, the materials thereof, the shapes thereof, the relativearrangement thereof, etc., and are disclosed simply as an example of anembodiment.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure will be describedhereinafter in detail with reference to the attached drawings, whereinthe like reference numerals refer to the like elements. The presentdisclosure may, however, be embodied in many different forms, and thusthe detailed description of the embodiment of the invention in view ofattached drawings should not be construed as being limited to theembodiment set forth herein; rather, these embodiments are provided sothat the present disclosure will be thorough and complete, and willfully convey the general concept of the disclosure to those skilled inthe art.

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

Respective dimension and shape of each components/members in thedrawings are only intended to exemplarily illustrate the contents of thedisclosure, rather than to demonstrate the practical dimension orproportion of components of the sealing arrangement solution.

FIG. 1 is a schematic perspective view illustrating a final product ofpower electronic device including a lead frame with power pins andauxiliary pins extending therefrom, in the prior art; and FIG. 2 is aschematic top view of a conventional lead frame in the prior art, beforeplacing onto a substrate of a power electronic device.

In the prior art, a lead frame is widely used in the power electronics,as illustrated in FIG. 1. To be specific, by way of example, asillustrated in FIG. 2, a conventional lead frame 1 for semiconductorchip is provided, comprising an outer supporting frame 2, a plurality ofcontrol leads 3 and a plurality of power leads 4.

The outer supporting frame 2 is formed to be a hollow metal sheet,comprising: a control-side beam 21 from which the plurality of controlleads 3 extend inwards; a power-side beam 22 from which the plurality ofpower leads 4 extend inwards, the control-side beam being parallel tothe power-side beam and aligned therewith at both ends; and a pair oflateral beams 23 each of which are interposed between correspondingaligned ends of the control-side beam 21 and the power-side beam 22,such that the outer supporting frame 4 is formed in a rectangularpattern with a central rectangular cavity 5 for accommodating asemiconductor therein.

The plurality of control leads 3 are arranged to be in parallel with andspaced apart from one another, extending perpendicular to thecontrol-side beam 21, and each of the plurality of control leads 3comprises a first outer lead section 31 and a first inner lead section32 aligned in line and joined together at a first central joint 33, withall of the first central joints being coupled by a first supporting bar34 stretching laterally across the pair of lateral beams 23 so as tosecure in place the plurality of control leads relative to the leadframe before a trimming process thereof which follows aattaching/bonding process of a semiconductor chip onto the lead frame.

Likewise, the plurality of power leads 4 are arranged to be in parallelwith and spaced apart from one another, extending perpendicular to thepower-side beam 22, and each of the plurality of power leads 4 comprisesa second outer lead section 41 and a second inner lead section 42aligned in line and joined together at a second central joint 43, withall of the second central joints being coupled by a second supportingbar 44 stretching laterally across the pair of lateral beams 23 so as tosecure in place the plurality of power leads relative to the lead framebefore a trimming process thereof which follows a attaching/bondingprocess of a semiconductor chip onto the lead frame.

Each of the first outer lead sections 31 is positioned between thecontrol-side beam 21 and corresponding first central joint 33, whileeach of the first inner lead sections 32 extends inwards of the leadframe 1 from the corresponding first central joint 33 and terminates ata free inner control terminal 35. And each of the second outer leadsections 41 is positioned between the power-side beam 22 andcorresponding second central joint 43, while each of the second innerlead sections 42 extends inwards of the lead frame 1 from thecorresponding second central joint 43 and terminates at a free innerpower terminal 45. And the semiconductor chip, which is to be attachedonto and bonded to the lead frame 1, is configured to be directlyattached to the free inner control terminals 35 of the first inner leadsections 32 and the free inner power terminals 45 of the second innerlead sections 42 of the lead frame 1.

As aforementioned, if a single lead frame formed by only one material isto be used, then a compromise should be reached, leading to power leadsthat have a greater than optimum resistance and press-fit leads which donot have optimum characteristics, due to different requirements of thepower and control leads.

In order to combine both elastic press-fit pins as control terminals andpower terminals with high current carrying capability into one singlemold module as an integral lead frame, it is advantageous to usedifferent materials for each pin type, since the use of differentmaterials for different pin types helps to tailor the properties likehigh tensile strength for the press-fit type and high current carryingcapability for the power terminals. Therefore, for example, it may beadvantageous to develop a lead frame with power leads of one highlyconductive material and press-fit control leads of another elasticconductive material, so that only one assembly lead frame has to beprocessed finally in a same manner as that used for previous lead framein the prior art, while maintaining existing molding, trimming andforming processes.

Fundamental Embodiment

FIG. 3 is a schematic top view of an exemplary lead frame with a powersub lead frame and a control sub lead frame which are formed bydifferent metallic materials in an exemplary embodiment of theinvention, before placing onto a substrate of a power electronic device;and FIG. 4(a)-4(e) are schematic top views illustrating the method ofattaching a semiconductor chip onto a substrate while forming individualfinal power terminals and control terminals, by using the exemplary leadframe in FIG. 3. The substrate 2022 may typically be formed from adirect copper bond (DCB) structure where a ceramic inner plate iscovered with a copper layer on both sides. When used in a power modulesuch as in the current invention, one of the copper layers may be usedfor the mounting of electrical components (and the lead frame), and thiscopper layer may be patterned to give track areas electrically insulatedfrom other track areas.

According to a general technical concept of the present invention, in anexemplary embodiment of the invention, there is provided a lead frame101, as illustrated in FIGS. 3, comprising one or more power terminals103 and one or more control terminals 104, at least one of the controlterminals 103 being externally terminated with a press-fit contactmember 1031, and at least one of the control terminals 103 and at leastone power terminals 104 being formed from different materials.

As an exemplary embodiment, to be specific, as illustrated in FIG. 3,the lead frame 101 of the present application comprises a control sublead frame 1011 for carrying control signals and a higher capacity powersub lead frame 1012 for carrying the main or rated current. By way ofexample, the control sub lead frame 1011 and the power sub lead frame1012 are individually manufactured and subsequently terminated or joinedtogether during manufacturing so as to form an integral lead frame 101.For example, either one of the control sub lead frame and the power sublead frame may be firstly stamped, and then processed by a series ofoptional steps including bending, drawing, forming or other metalworkingprocesses to form their respective final patterns individually.

Moreover, in an exemplary embodiment of the invention, a material of thecontrol sub lead frame 1011 is different from that of the power sub leadframe 1012. For example, the control sub lead frame 1011 may be formedby a conductive material with certain elasticity for facilitatingpress-fit terminals for carrying low-level control signals; and thepower sub lead frame 1012 may be formed by a conductive metallicmaterial with lower resistance and thus high current carryingcapability. By way of example, the power leads with power connectionterminals are preferably made from pure copper, or alternatively itsalloy with similar optimum conductive properties, e.g., Wieland K12Copper Cu-HCP , or K14 Cu-PHC which may be commercially available fromWieland Metals Inc.; while the control leads with press-fit terminalsare preferably made from a material has a certain amount of elasticity,i.e., high tensile strength, as compared with pure copper, e.g., a highperformance alloy K55 or B16 (phosphor bronze) which is commerciallyavailable from Wieland Metals Inc. Note that stating a component is madeof a metal material essentially includes components made from pure metalor from alloys of such metal materials).

To be specific, by way of example, as shown in FIG. 3, the control sublead frame 1011 comprises a control-side beam 1021, a pairs of lateralbeams 1023 which extend inwards the lead frame 101 at both ends of thecontrol-side beam 1021, and a plurality of control terminals 103 whichextend inwards from and perpendicular to the control-side beam 1021.Likewise, the power sub lead frame 1012 comprises a power-side beam1022, a pairs of lateral beams 1024 which extend inwards the lead frame101 at both ends of the power-side beam 1022, and a plurality of powerterminals 104 which extend inwards from and perpendicular to thepower-side beam 1022. All the beams 1021, 1023 of the control sub leadframe 1011, and all the beams 1022, 1024, are coordinately formed as apattern of a hollow rectangular metal sheet of two metallic materials,with a central rectangular cavity 105 for accommodating a semiconductortherein.

Here, in an exemplary embodiment of the invention, as illustrated inFIG. 3 in details, the plurality of control terminals 103 are arrangedto be in parallel with and spaced apart from one another, and each ofthe plurality of control terminals 103 comprises a first outer leadsection 1031 and a first inner lead section 1032 aligned in line andjoined together at a first central joint 1033, with all of the firstcentral joints 1033 being coupled crosswise by a first supporting bar1034 stretching laterally across the pair of lateral beams 1023 so as tosecure in place the plurality of control terminals 103 relative to thelead frame 101 before a trimming process thereof which follows aattaching/bonding process of a semiconductor chip onto the lead frame.

Likewise, by way of example, as also illustrated in FIG. 3 in details,the plurality of power terminals 104 are arranged to be in parallel withand spaced apart from one another, and each of the plurality of powerterminals 104 comprises a second outer lead section 1041 and a secondinner lead section 1042 aligned in line and joined together at a secondcentral joint 1043, with all of the second central joints 1043 beingcoupled crosswise by a second supporting bar 1044 stretching laterallyacross the pair of lateral beams 23 so as to secure in place theplurality of power terminals 104 relative to the lead frame 101 before atrimming process thereof which follows a attaching/bonding process of asemiconductor chip onto the lead frame.

In an exemplary embodiment of the invention, each of the first outerlead sections 1031 is positioned between the control-side beam 1021 andcorresponding first central joint 1033 and functions as a press-fitcontact member after being trimmed to separate from adjacent first outlead sections, in other words, each control terminal 103 is externallyterminated with a press-fit contact member 1031; while each of the firstinner lead sections 1032 extends inwards of the lead frame 101 from thecorresponding first central joint 1033 and terminates at a free controlcontact member 1035. And each of the second outer lead sections 1041 isfor example positioned between the power-side beam 1022 andcorresponding second central joint 1044, while each of the second innerlead sections 1042 extends inwards of the lead frame 101 from thecorresponding second central joint 1043 and terminates at a free powercontact member 1045.

According to an exemplary embodiment, during manufacturing of the leadframe 101, since the control sub lead frame 1011 and the power sub leadframe 1012, which are formed by different metallic materials, areindividually manufactured and subsequently joined and bonded together soas to form an integral lead frame 101, in other words, the lead frame101 includes a bimetallic structure, generally including the control sublead frame 1011 and the power sub lead frame 1012 which meets with thecontrol sub lead frame 1011 at a bimetallic interface 106, asillustrated in FIG. 3. The bimetallic interface 106 is defined along allof abutting portions of the lateral beams 1023 of the control sub leadframe 1011 and the corresponding lateral beams 1024 of the power sublead frame 1012. In a fundamental exemplary embodiment, the bimetallicinterface 106 is coincident with the bonding interface, e.g., thewelding interface, between the ends of lateral beams 1023, 1024 of twosub lead frames.

During the application of the lead frame 101, for example, FIG.4(a)-4(g) are schematic top views illustrating the method of attaching asemiconductor chip onto a substrate while forming individual final powerterminals and control terminals, by using the exemplary lead frame inFIG. 3. By way of example, before placement of the lead frame 101 andits associated power module and connections onto the substrate, firstly,some electronic components 2021 such as semiconductors, resistors,diodes, capacitors or inductors are firstly placed onto the substrate,as illustrated in FIGS. 4(a) and 4(b). Then the lead frame 101 isattached onto the substrate, with its terminals being arrangedcompletely within an area of the substrate, as shown in FIG. 4(c). Then,additional components may be mounted and interconnections such aswire-bonds, ribbon bonds or other connection methods known in the fieldmay be made between the components, the circuit track elements of thesubstrate and between the components, track elements and terminals ofthe lead frame. After this, as further illustrated in FIG. 4(d), a mould2023 of the package of the power module may be directly disposed tooverlap the lead frame, especially by overlapping, covering and in turnattaching/bonding to its terminals. Hereafter, a trimming process isfollowed, as illustrated in FIG. 4(e), to separate all of theinterconnected leads/terminals, e.g., by removing all the first andsecond central joints 1033, 1043 while removing all the outer frame,i.e., beams 1021, 1022, 1023, 1024, of the lead frame 101. Finally, asillustrated in side cross sectional views of FIGS. 4(f), 4(g),individual leads or terminals 103, 104 may then be bent to complete thepins for connection to other outer circuits and/or components.

Likewise, on the basis of above embodiment, some variations,modifications and alterations can be realized, for example, thethickness of the different materials is essentially the same.

And as far as the combination between the two sub lead frames areconcerned, an interface for combination can be exemplified in variousmodifications, as set forth in details hereinafter.

Bimetallic Interface Embodiment I

FIG. 5(a) illustrates a partially enlarged schematic cross-sectionalview of the lead frame as illustrated in FIG. 3, at its bimetallicinterface 106 where the power sub lead frame 1012 and the control sublead frame 1011 are bonded directly together, according to an embodimentof the present invention.

In an exemplary embodiment of the invention, the power sub lead frame1012 formed by a metallic material, either a pure metal or its alloy,and the control sub lead frame 1011 which is formed by a differentmetallic material, are placed to abut directly and tightly against eachother at ends and subsequently bonded/jointed together, e.g., by anumber of available technologies including laser welding, ultrasonicwelding, cladding, or use of epoxy resins, other welding means, or anyother attaching means, to form the bimetallic interface 106. Hereby, thebimetallic interface 106 is defined along all abutting portions of thepower sub lead frame 1012 and the control sub lead frame 1011, i.e., atthe end faces of all the lateral beams 1023, 1024 thereof, and thus maybe considered as being coincident with the bonding interfacetherebetween.

By way of the direct abutting and subsequently applied bonding/jointingmethods, it may be ensured that the two sub lead frames are securelybond together to form an integral and secured lead frame with both thehigh conductivity property at power terminals but also high elasticityat control terminals for press-fit.

Bimetallic Interface Embodiment II

FIG. 5(b) illustrates a partially enlarged schematic cross-sectionalview of the lead frame as illustrated in FIG. 3, at its bimetallicinterface 106 where the power sub lead frame 1012 and the control sublead frame 1011 are bonded together by inserting free end portions ofone sub lead frame into the profiles of free end portions of another sublead frames, according to another embodiment of the present invention.

The lead frame of the Bimetallic Interface Embodiment II as illustratedin FIG. 5(b) only differs from that of the Bimetallic InterfaceEmbodiment I as illustrated in FIG. 5(a) in the specific structure atthe bimetallic interface.

Alternatively, in an exemplary embodiment of the invention, theaforementioned bimetallic interface as in FIG. 5(a) is formed to abuteach other at ends of the lateral beams directly. In contrast, asillustrated in FIG. 5(b), along the intended bimetallic interface, theends of the lateral beams 1023 of the control sub lead frame 1011 may bemechanically and electrically connected to the ends of the lateral beams1024 of the power sub lead frame 1012 by cladding, or be terminatedtogether by other processes such as by a number of availabletechnologies including laser welding, ultrasonic welding, cladding, oruse of epoxy resins, other welding means, or any other attaching means,to form the bimetallic interface 106.

In an exemplary embodiment, the ends of the lateral beams 1023 of thecontrol sub lead frame 1011 may be formed with a pocket defined alongand within the envelope or profile of such ends forreceiving/accommodating therein the ends of the lateral beams 1024 ofthe power sub lead frame 1012. The ends of the lateral beams 1024 areinserted into the pocket and fits within the envelope or profile of theends of the lateral beams 1023. The ends of the lateral beams 1024 aresmaller as compared with the ends of the lateral beams 1023, in widthand/or height, and the ends of the lateral beams 1023 extend the fullscope of the ends of the lateral beams 1024, so as to define thebimetallic interface therebetween. Subsequently, the two sub lead frames1011, 1012 are bonded/jointed together at ends of lateral beams 1023,1024, e.g., by a number of available technologies including laserwelding, ultrasonic welding, cladding, or use of epoxy resins, otherwelding means, or any other attaching means, to form the bimetallicinterface 106. By way of example, due to the existence of pocket and thedifference in width and/or height of the end of lateral beams 1023,1024, the bimetallic interface 106 thus may be considered as being notcoincident with the bonding interface therebetween. Such condition alsoapplies when the respective structures of the ends of both pairs oflateral beams 1023, 1024 replace each other, vice versa.

By way of the provision of pocket at ends of one lateral beam forreceiving corresponding ends of another opposed lateral beam, andsubsequent bonding/jointing methods, it is appreciated by those skilledin the art that, the two sub lead frames fit each other positively andbond together securely, to form an integral and secured lead frame withboth the high conductivity property at power terminals but also highelasticity at control terminals for press-fit.

Bimetallic Interface Embodiment III

FIG. 6(a) illustrates a partially enlarged schematic top view of abimetallic interface 106 of lead frame as illustrated in FIG. 3, wherethe power sub lead frame 1012 and the control sub lead frame 1011 arefirstly fitted with each other positively and then bonded together,according to still another embodiment of the present invention.

The lead frame of the Bimetallic Interface Embodiment III as illustratedin FIG. 6(a) only differs from those of the Bimetallic InterfaceEmbodiments I, II and III as illustrated in FIGS. 5(a), 5(b) in thespecific structure at the bimetallic interface.

In an exemplary embodiment of the invention, the power sub lead frame1012 formed by a metallic material, either a pure metal or its alloy,and the control sub lead frame 1011 which is formed by a differentmetallic material, are firstly formed to be complementarily profiled attheir respective ends of the corresponding lateral beams 1023, 1024therebetween, e.g., by having respective concave/convex portions whichmay be complement in shape. And these two sub lead frames 1011 and 1012are subsequently placed to fit positively at the ends of theircorresponding lateral beams 1023, 1024 and to abut directly and tightlyagainst each other at ends, so as to define a predetermined position ofthe bimetallic interface therebetween.

Subsequently, the two sub lead frames are bonded/jointed together alongthe bimetallic interface, e.g., by a number of available technologiesincluding laser welding, ultrasonic welding, cladding, or use of epoxyresins, other welding means, or any other attaching means, to form thebimetallic interface 106. Hereby, the bimetallic interface 106 isdefined along all abutting portions of the power sub lead frame 1012 andthe control sub lead frame 1011, i.e., at the end faces of all thelateral beams 1023, 1024 thereof, and thus may be considered as beingcoincident with the bonding interface therebetween.

Through the use of both positive fit via complementarily profiled endsof corresponding lateral beams 1023, 1024 of the two sub lead frames,and the bonding/jointing methods, it may be ensured that the two sublead frames are securely bond together to form an integral and securedlead frame with both the high conductivity property at power terminalsbut also high elasticity at control terminals for press-fit.

Bimetallic Interface Embodiment IV

FIG. 6(b) illustrates a partially enlarged schematic top view of abimetallic interface 106 of lead frame as illustrated in FIG. 3, wherethe power sub lead frame 1012 and the control sub lead frame 1011 arefirstly fitted with and inserted into the profiles of each other,positively, and then bonded together, according to yet anotherembodiment of the present invention.

The lead frame of the Bimetallic Interface Embodiment IV as illustratedin FIG. 6(b) only differs from those of the Bimetallic InterfaceEmbodiments I, II and III as illustrated in FIGS. 5(a), 5(b) and 6(a) inthe specific structure at the bimetallic interface.

To be specific, in contrast, as illustrated in FIG. 6(b). In anexemplary embodiment of the invention, the power sub lead frame 1012formed by a metallic material, either a pure metal or its alloy, and thecontrol sub lead frame 1011 which is formed by a different metallicmaterial, are firstly formed to be complementarily profiled at theirrespective ends of the corresponding lateral beams 1023, 1024therebetween, e.g., by having respective concave/convex portions whichmay be complement in shape. And these two sub lead frames 1011 and 1012are subsequently placed to fit positively at the ends of theircorresponding lateral beams 1023, 1024 and to abut directly and tightlyagainst each other at ends, so as to define a predetermined position ofthe bimetallic interface therebetween.

Meanwhile, along the intended bimetallic interface, the ends of thelateral beams 1023 of the control sub lead frame 1011 may bemechanically and electrically connected to the ends of the lateral beams1024 of the power sub lead frame 1012 by cladding, or be terminatedtogether by other processes such as by a number of availabletechnologies including laser welding, ultrasonic welding, cladding, oruse of epoxy resins, other welding means, or any other attaching means,to form the bimetallic interface 106.

In an exemplary embodiment, the ends of the lateral beams 1023 of thecontrol sub lead frame 1011 may be formed with a pocket defined alongand within the envelope or profile of such ends forreceiving/accommodating therein the ends of the lateral beams 1024 ofthe power sub lead frame 1012. The ends of the lateral beams 1024 areinserted into the pocket and fits within the envelope or profile of theends of the lateral beams 1023. The ends of the lateral beams 1024 aresmaller as compared with the ends of the lateral beams 1023, in widthand/or height, and the ends of the lateral beams 1023 extend the fullscope of the ends of the lateral beams 1024, so as to define thebimetallic interface therebetween. Subsequently, the two sub lead frames1011, 1012 are bonded/jointed together at ends of lateral beams 1023,1024, e.g., by a number of available technologies including laserwelding, ultrasonic welding, cladding, or use of epoxy resins, otherwelding means, or any other attaching means, to form the bimetallicinterface 106. By way of example, due to the existence of pocket and thedifference in width and/or height of the end of lateral beams 1023,1024, the bimetallic interface 106 thus may be considered as being notcoincident with the bonding interface therebetween. Such condition alsoapplies when the respective structures of the ends of both pairs oflateral beams 1023, 1024 replace each other, vice versa.

By way of the provision of not only positive fit via complementarilyprofiled concave/convex shape at ends of corresponding lateral beams1023, 1024 of the two sub lead frames, but also pocket at ends of onelateral beam for receiving corresponding ends of another opposed lateralbeam, and subsequent bonding/jointing methods, it may be ensured thatthe two sub lead frames fit each other positively and bond togethersecurely, to form an integral and secured lead frame with both the highconductivity property at power terminals but also high elasticity atcontrol terminals for press-fit.

FIG. 7 illustrates a flow chart of a method for fabricating an exemplarylead frame by two different metallic materials.

According to another aspect of the exemplary embodiment of the presentinvention, as illustrated in FIG. 7, a method for fabricating the leadframe is also provided, comprising:

Step S101: manufacturing a control sub lead frame and a power sub leadframe individually and separately;

Step S102:forming one or more power terminals 103 within the power sublead frame and one or more control terminals 104 within the control sublead frame, individually;

Step S103: terminating at least one of the control terminals 103externally with a press-fit contact member 1031; and

Step S104: abutting, fitting and bonding/jointing the two sub leadframes together to form a secured bimetallic interface therebetween, soas to form an integral lead frame 101.

Further Embodiment

FIG. 8 is a schematic top view of an exemplary lead frame with a powersub lead frame and a control sub lead frame which are formed bydifferent metallic materials in a further embodiment of the invention,before placing onto a substrate of a power electronic device;

In this embodiment, the control sub lead frame is confined to theimmediate area around the sections of the sub lead frame that will formthe press-fit contacts. Such an embodiment illustrates the idea thatsmall sections of the full lead frame may be constructed from differentmaterials, rather than the lead frame being divided roughly in half,with one half comprising one material and the other half comprisinganother. It will also be obvious that there can be more than twoseparate material sections used in the final lead frame. Two, three,four or more separate sub lead frames comprising different materials canbe connected together to form the final lead frame. In this way, veryprecise materials can be used where required in the manner describedabove.

In conclusion, due to aforementioned exemplary embodiment of a leadframe with both a control sub lead frame and a power sub lead framewhich are formed by different metallic materials, one with a highcurrent conductivity and the other with a certain elasticity property,as well as the unique structure at bonding surfaces of the two sub leadframes via bimetallic interface, a novel and advantageous lead-frame,and a method for fabricating the same are provided, having someadvantageous technical effects, as below: firstly, the use of differentmaterials for different pin types helps to tailor the properties likehigh tensile strength for the press-fit type signal terminals or controlterminals and high current carrying capability and electricalconductivity property for the power terminals, therefore the lead-framematerial may not necessarily be any one specific alloy material whichhas to make compromise between electrical resistance and mechanicalstrength. Secondly, in the power terminals, low material cross sectionscan be realized because of the better electrical conductivity ascompared with alloys with higher mechanical strengths; meanwhile, aminimized dimensional difference between the power terminals and thecontrol or signal terminals may advantageously balance between the powerterminals and the control or signal terminals the distribution of notonly internal stresses but also any external forces applied thereon,respectively. Thirdly, several different plating processes could also beincorporated during fabrication of a lead-frame as a function of theindividual needs of the different pin types, without the need of masksin the plating process. Finally, since such lead-frame can be achievede.g. by combining at least two or more sub-lead frames to one part sothat only one assembled lead frame has to be processed same as partsmade of prior art, hereby, an advantage of this can be obtained suchthat the molding, trimming, and pin-forming processes still remain thesame as that of the conventional lead-frame processing.

Although the disclosure is described in view of the attached drawings,the embodiments disclosed in the drawings are only intended toillustrate the preferable embodiment of the present inventionexemplarily, and should not be deemed as a restriction thereof.

Various embodiments of the present invention have been illustratedprogressively, the same or similar parts of which can be referred toeach other. The differences between each embodiment and the others areemphatically described.

It should be noted that the terms, such as “comprising”, “including” or“having”, should be understood as not excluding other elements or stepsand the word “a” or “an” should be understood as not excluding plural ofsaid elements or steps. Further, any reference number in claims shouldbe understood as not limiting the scope of the present invention.

It should be appreciated for those skilled in this art that the aboveembodiments are intended to be illustrated, and not restrictive. Forexample, many modifications may be made to the above embodiments bythose skilled in this art, and various features described in differentembodiments may be freely combined with each other without conflictingin configuration or principle.

Although several exemplary embodiments of the general concept of thepresent invention have been shown and described, it would be appreciatedby those skilled in the art that various changes or modifications may bemade in these embodiments without departing from the principles andspirit of the disclosure, the scope of which is defined in the claimsand their equivalents.

While the present disclosure has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisdisclosure may be made without departing from the spirit and scope ofthe present disclosure.

What is claimed is:
 1. A lead frame, comprising one or more powerterminals and one or more control terminals, wherein at least one of thecontrol terminals is externally terminated with a press-fit contactmember, and wherein at least one of the control terminals and at leastone power terminals are formed from different materials.
 2. The leadframe according to claim 1, wherein the lead frame comprises at leastone power sub lead frame which is formed by a first material with highcurrent conductivity and at least one control sub lead frame which isformed by a second material with elasticity for making press-fit typeterminals thereof, and wherein at least one power sub lead frame and atleast one control sub lead frame are combined together at a bimetallicinterface.
 3. The lead frame according to claim 2, wherein the power sublead frame and the control sub lead frame which abut each other arebonded together at the bimetallic interface.
 4. The lead frame accordingto claim 3, wherein the power sub lead frame and the control sub leadframe are bonded together by any one chosen from a group comprisinglaser welding, ultrasonic welding, cladding, or use of epoxy resins. 5.The lead frame according to claim 2, wherein one of the sub lead framesis formed to be provided with a pocket at an end thereof along thebimetallic interface for receiving full profile of a correspondingportion of the other sub lead frame.
 6. The lead frame according toclaim 5, wherein the power sub lead frame and the control sub lead frameare bonded together by any one chosen from a group comprising laserwelding, ultrasonic welding, cladding, or use of epoxy resins.
 7. Thelead frame according to claim 2, wherein edges of the power sub leadframe and the control sub lead frame at the bimetallic interface areformed to be complementarily profiled along the bimetallic interface, byhaving respective concave/convex portions which are complement in shape.8. The lead frame according to claim 7, wherein the power sub lead frameand the control sub lead frame are bonded together by any one chosenfrom a group comprising laser welding, ultrasonic welding, cladding, oruse of epoxy resins.
 9. The lead frame according to claim 7, wherein oneof the sub lead frames is formed to be provided with a pocket at an endthereof for receiving full profile of corresponding portion of the othersub lead frame, along all of the complementarily profiled edges of thepower sub lead frame and the control sub lead frame.
 10. The lead frameaccording to claim 9, wherein the power sub lead frame and the controlsub lead frame are bonded together by any one chosen from a groupcomprising laser welding, ultrasonic welding, cladding, or use of epoxyresins.
 11. The lead frame according to claim 1, wherein the thicknessof the first and second materials is essentially the same.
 12. A methodfor fabricating a lead frame, comprising steps of: manufacturing acontrol sub lead frame and a power sub lead frame individually andseparately; forming one or more power terminals within the power sublead frame and one or more control terminals within the control sub leadframe, individually; terminating at least one of the control terminalsexternally with a press-fit contact member; and abutting, fitting andbonding the two sub lead frames together to form a secured bimetallicinterface therebetween so as to form an integral lead frame, wherein atleast one of the control terminals and at least one power terminals areformed from different materials.
 13. The method according to claim 12,wherein the step of forming terminals further comprises: terminating atleast one of the control terminals internally with a control contactmember; and terminating at least one of the power terminals internallywith a power contact member.
 14. The method according to claim 12,wherein the step of manufacturing the two sub lead frames comprisesproviding a pocket at an end thereof along the bimetallic interface forreceiving full profile of corresponding portion of the other sub leadframe.
 15. The method according to claim 12, wherein the step ofmanufacturing the two sub lead frames comprises forming edges of thepower sub lead frame and the control sub lead frame at the bimetallicinterface to be complementarily profiled along the bimetallic interface,by having respective concave/convex portions which are complement inshape.
 16. The method according to claim 12, wherein the step ofabutting, fitting and bonding the two sub lead frames together comprisesbonding by any one chosen from a group comprising laser welding,ultrasonic welding, cladding, or use of epoxy resins.
 17. The methodaccording to claim 12, wherein the lead frame comprises a power sub leadframe which is formed by a first material with high current conductivityand a control sub lead frame which is formed by a second material withelasticity for making press-fit type terminals thereof, and wherein thepower sub lead frame and the control sub lead frame are combinedtogether at a bimetallic interface.
 18. The method according to claim12, wherein the thickness of the first and second materials isessentially the same.